did a little google search

"Bolt-action sporting rifles in various popular calibers carrying the Whitworth name were made from the late 1960s to 1997. The information I have indicates they were assembled at Manchester, England until 1980, using Mark X Mauser-type actions imported from Yugoslavia. After 1980 the complete rifles were made in Yugoslavia. Some models still carried the Whitworth name but were marked as made in Yugoslavia rather than at Manchester.
I’ve also heard of Whitworth rifles made at Manchester using military surplus model 1917 “Enfield” actions, but have never seen one, even in pictures.

Your rifle appears to have been made at Manchester and the markings you mention are British proof marks. I don’t know what action your rifle has, but if it is the Mark X action it would be a Mauser type with a swept-back bolt handle. Also, 1917 actions had a dogleg bolt handle.

From about 1970 to 1997 Interarms imported these rifles into the US with various model names such as Viscount, Cavalier, and Whitworth Express. They are considered to be good quality hunting rifles comparable to popular US made bolt-action hunting rifles. The current Blue Book suggests values of $375 to $475 for 100 per cent condition Mark X Whitworth rifles made in Yugoslavia, and a “slight premium” for those made in England. There is no particular collector interest at this time and their value is as well made sporting rifles. —Dave Anderson"

http://www.westernsportsman.com/faqs/q-w...you-may-be-abl/

when remembering british traditions there can be no doubt that someone had or bought the Whitworth firm in the 1960 and use it only for trade or also for making some guns.

http://www.peterdyson.co.uk/acatalog/TRADE-LABELS-BRITISH-1.html

it seems they made or marketed ( made in Birmingham?) also some better quality express rifles like this 404

"

*WHITWORTH MAUSER ACTION CUSTOM 404 JEFFERY RIFLE. SN A284051. Cal. 404 Jeffery. 23″ Tapered round bbl has one standing, three folding leaf express sight marked for 100, 200, and 300 yards, dovetailed through island base. Sleeved-on matted front ramp is fitted with gold bead front sight with pop-up porcelain night bead. Knurled steel sight cover is fitted. Sling loop is soldered to bottom of bbl. Whitworth marked Interarms “CZ” action with Virginia and Manchester England addresses, has engine turned bolt body and extractor. Standard bottom metal with hinged floorplate and button release in bow, has had floorplate engraved with well cut shaded scroll, and with silver wire inlay framing savanna scene with large silver inlaid charging rhino. Classically styled custom stock appears to be figured mesquite, and measures 13-3/8″ over black “Old English” rifle pad. Rifle features large right hand cheekpiece, nicely cut 28 LPI borderless point pattern checkering, hard rubber forend tip, and engraved steel grip cap with monogram “WC” relief inlaid in gold. Drop at heel: Approx 2-1/4″, drop at comb: approx 1-3/4″. Weight: 8 lbs. 4 oz, LOP 13-3/8″. CONDITION: Excellent, as built with only a few minor marks in wood, and compression in left side forend checkering. Bore is excellent. 404 Jeffery is one of the most highly regarded big game cartridges of all time. 4-41131 MGM55 (1,000-1,500) "
http://jamesdjulia.com/item/lot-1106-whitworth-mauser-action-custom-404-jeffery-rifle-41131/
you can learn something new every day